The present invention generally relates to the construction industry and, in particular, to a method and apparatus for shoring of open excavation sites.
Excavation workers are exposed to many hazards perhaps the chief of which is the danger of cave-ins. As a result, the United States Department of Labor Occupational Safety and Health Administrations (OSHA) requires that all excavations be prepared for the protection of employees exposed to potential cave-ins. Acceptable excavation site preparations include sloping or benching of the sides of the excavation, supporting the sides of the excavation, or placing a shield between the side of the excavation and the work area.
Each of these methods of protecting workers is dependent upon factors such as soil classification, depth of cut, water content of the soil, changes due to weather and climate, and other operations in the vicinity of the excavation. It can be dangerous, therefore, to design a system for protecting workers which meets only minimum standards. This is because over time, conditions which prevail when a system is designed can change, rendering the designed system insufficient for later prevailing conditions.
A typical operation requiring excavation and, therefore, protection of workers at the excavation site is the installation of underground storage tanks. These tanks are manufactured in various sizes. Typically, oil companies install three 10,000 gallon double wall fiberglass tanks at a location where oil is to be stored. Presently, the tanks are installed by a procedure which includes excavating a tank hole which is approximately thirty-six feet long by thirty-two feet wide by fourteen feet deep. Depending on a given application, the excavation of the new tank hole may be preceded by the removal of old storage tanks already in place. In any case, once the new tank hole is excavated, a twelve inch thick concrete pad is poured to which the tanks are anchored. On top of the concrete pad a twelve inch thick layer of peastone is placed. The new tanks are installed over the peastone and the excavated site is backfilled to grade.
A known method for shoring an operation such as this includes driving sheet piling in a rectangle approximately thirty feet by thirty-six feet by twenty feet deep. Once this is completed, a tank installer excavates inside the rectangular shoring to a depth of approximately fourteen feet below grade. The site is then prepared and the tanks installed similarly to the manner described above. After tank installation, the rectangular shoring is either cut down to about five feet below grade and buried during backfilling or it is removed from the ground. This method of shoring an excavation site is very time consuming and expensive, typically costing between forty and fifty thousand dollars and adding three days to a tank replacement project.
Another method for shoring an excavation site is described in U.S. Pat. No. 4,685,837 (Cicanese, Aug. 11, 1987). This patent describes a multi-sided portable trench and pit form system having at least two panels forming each side. The panels are releasably interconnectable along the vertical margins of each adjacent panel and side. It is a lightweight system that is typically assembled inside of the excavation site. As a result, in addition to exposing workers to the risk of cave-in during assembly of the shoring system, the system is not suitable for excavations where soil conditions dictate the need for high strength shoring.
It is, therefore, an object of the invention to provide a method and apparatus for shoring an excavation site that can be quickly and inexpensively practiced while providing high strength protection against cave-ins. It is another object of the invention to provide such an apparatus that can be recycled for multiple uses.